Acoustic Touch Sensor

ABSTRACT

A touch sensor comprises a substrate capable of propagating acoustic waves and includes a first surface having a touch sensitive region. A first sidewall intersects the first surface along a first edge. The first edge is configured to propagate a first acoustic wave along the first edge. The first acoustic wave may be a one-dimensional edge wave. A wave converter converts the first acoustic wave to a second acoustic wave, and the first surface is configured to propagate the second acoustic wave across the touch sensitive region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.11/106,394, which claimed priority from U.S. Provisional PatentApplication Ser. No. 60/562,461, entitled “Acoustic Touch Sensor,” filedApr. 14, 2004, and U.S. Provisional Patent Application Ser. No.60/562,455, entitled “Acoustic Touch Sensor,” filed Apr. 14, 2004, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to touch sensors, in particular to acoustic touchsensors and acoustic touchscreens having narrow functional borders andincreased touch-sensitive areas.

2. Introduction to the Invention

An acoustic touch sensor has a touch sensitive area on which thepresence and location of a touch is sensed by the touch's effect on thetransmission of acoustic waves across a touch sensor substrate. Acoustictouch sensors may employ Rayleigh waves (including quasi-Rayleighwaves), Lamb or shear waves, or a combination of different types of theacoustic waves.

FIG. 1 illustrates the operation of a conventional acoustic touchsensor, an acoustic touchscreen 1. The touchscreen 1 has atouch-sensitive area 2 inside of which two-dimensional coordinates oftouches are determined. For example, the touch-sensitive area 2 mayinclude the region bounded by the dashed line 16 which represents theinner boundary of a bezel 10. A first transmitting transducer 3 a ispositioned outside of touch-sensitive area 2 and is acoustically coupledto the surface of touchscreen 1. The transducer 3 a sends an acousticsignal in the form of an acoustic wave 11 a traveling parallel to thetop edge of touchscreen 1 and generally in the plane of touchscreen 1.Aligned in the transmission path of acoustic wave 11 a is a first lineararray 13 a of partially acoustically reflective elements 4, each ofwhich partially transmits the acoustic signals and partially reflectsthem (by an angle of approximately 90°), creating a plurality ofacoustic waves (e.g., 5 a, 5 b and 5 c) traveling vertically acrosstouch-sensitive area 2. The spacing of reflective elements 4 is variableto compensate for the attenuation of the acoustic signals withincreasing distance from first transmitter 3 a. It is also well knowneven if reflective elements 4 are uniformly spaced, signal equalizationmay be achieved by varying the reflective strength of reflectiveelements 4. Acoustic waves 5 a, 5 b, and 5 c are again reflected by anangle of approximately 90° (see arrow 11 b) by a second linear array 13b of partially acoustically reflective elements 4 towards a firstreceiving transducer 6 a upon reaching the lower edge of touchscreen 1.At the receiving transducer 6 a, the waves are detected and converted toelectrical signals for data processing. Similar arrangements ofreflective elements are located along the left and right edges oftouchscreen 1. A second transmitting transducer 3 b generates anacoustic wave 12 a along the left edge, and a third linear array 13 c ofpartially acoustically reflective elements 4 creates a plurality ofacoustic waves (e.g., 7 a, 7 b, and 7 c) traveling horizontally acrosstouch-sensitive area 2. Acoustic waves 7 a, 7 b, and 7 c are redirectedalong 12 b by a fourth linear array 13 d of partially acousticallyreflective elements 4 towards receiving transducer 6 b, where they aredetected and converted to electrical signals for data processing.

If touch-sensitive area 2 is touched at position 8 by an object such asa finger or stylus, a portion of the energy of the acoustic waves 5 band 7 a is absorbed by the touching object. The resulting attenuation isdetected by receiving transducers 6 a and 6 b as a perturbation in theacoustic signal. A time delay analysis of the data with the aid of amicroprocessor (not shown) allows determination of the coordinates oftouch position 8. The device of FIG. 1 can also function as atouchscreen with only two transducers using a transmit/receivetransducer scheme.

A housing 9, indicated by dashed lines in FIG. 1, may be associated withtouchscreen 1. The housing can be made of any suitable material, forexample molded polymer or sheet metal. The housing 9 includes a bezel10, indicated by dashed line 16 representing an inner boundary of bezel10 and dashed line 17 indicating an outer boundary of bezel 10 inFIG. 1. The inner dashed line 16 shows that the housing 9 overlays aperiphery of touchscreen 1, concealing the transmitting and receivingtransducers, the reflective elements, and other components, but exposingtouch-sensitive area 2. This arrangement can protect the concealedcomponents from contamination and/or damage, provide an aestheticappearance, and define the touch-sensitive area for the user.

A touchscreen may comprise a separate faceplate overlaid on a displaypanel. The faceplate is typically made of glass, but any other suitablesubstrate may be used. The display panel may be a cathode ray tube(CRT), a liquid crystal display (LCD), plasma, electroluminescent,organic light-emitting-diode (OLED) display, or any other type ofdisplay.

As shown in FIG. 1, the touch sensitive area 2 is surrounded by borderregions 15 where the reflective elements 4 and the transmitting andreceiving transducers 3 a, 3 b, 6 a and 6 b are located. Reducing thewidth of border regions 15 increases the touch sensitive area 2. Fortouch sensor applications using transparent touch sensors such astouchscreens, the width of the border can be especially important. Atouch sensor with narrowed border regions 15 can be integrated intodisplay monitors that themselves have a narrow border around thedisplayed image. This feature is desirable as the general market trendfor devices such as monitors is towards sleeker and more mechanicallycompact designs. A touch sensor with narrowed border regions 15 also ismore easily sealed as well as being lighter and can have increasedsensor area. Amongst competing touchscreen technologies, (e.g.,acoustic, capacitive, resistive and infrared) acoustic touchscreens tendto have wider borders.

It is possible to reduce the border region of a touchscreen by using awaveguide to concentrate an acoustic wave in the border region, asdisclosed in U.S. Pat. No. 6,636,201, the disclosure of which isincorporated herein by reference. However, alternate solutions may bedesired which do not require providing a waveguide on the touch surfaceof the touch sensor substrate.

For the reasons outlined above, it is desirable to have acoustic touchsensor designs capable of accommodating a very narrow border region.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a touch sensor comprises a substrate. The substrateis capable of propagating acoustic waves and includes a first surfacehaving a touch sensitive region. A first sidewall intersects the firstsurface along a first edge. The first edge is configured to propagate afirst acoustic wave along the first edge, and the first surface isconfigured to propagate a second acoustic wave across the touchsensitive region. A wave converter converts the first acoustic wave tothe second acoustic wave, and the second acoustic wave is based on thefirst acoustic wave. Optionally, the wave converter may be a reflectivearray that coherently scatters and mode converts the first acoustic waveinto the second acoustic wave.

In another embodiment, a touch sensor system comprises a transmitter forgenerating a one-dimensional first acoustic wave. A touch sensorcomprises a substrate capable of propagating acoustic waves. Thesubstrate includes a first surface having a touch sensitive region.First and second sidewalls intersect the first surface along first andsecond edges. The first edge is configured to propagate the firstacoustic wave and the first surface is configured to propagate a secondacoustic wave across the touch sensitive region. A first converter isprovided on the substrate for converting the first acoustic wave to thesecond acoustic wave. A detector is provided on the substrate fordetecting the second acoustic wave after traversing at least a portionof the touch sensitive region. Such detection of the second acousticwave may be direct or indirect.

In another embodiment, a method is provided for detecting a touch on atouch sensitive region of a substrate capable of propagating acousticwaves. The substrate includes a first surface having the touch sensitiveregion. First and second sidewalls of the substrate intersect the firstsurface along first and second edges. The method comprises transmittinga one-dimensional first acoustic wave along the first sidewall. Thefirst acoustic wave is converted into a second acoustic wave. The secondacoustic wave is directed along the first surface through the touchsensitive region. The second acoustic wave is detected proximate thesecond sidewall of the substrate. Such detection of the second acousticwave may be direct or indirect.

In another embodiment, a touch sensor comprises a substrate capable ofpropagating acoustic waves. The substrate includes a first surfacehaving a touch sensitive region and a first sidewall intersecting thefirst surface along a first edge. The first edge is configured topropagate a first acoustic wave along the first edge, and the firstsurface is configured to propagate a second acoustic wave across thetouch sensitive region. The second acoustic wave is based on the firstacoustic wave. The touch sensor further comprises a reflective arrayhaving reflector elements formed on the substrate for mode conversionbetween the first and second acoustic waves. The first edge may form acurved region. The touch sensitive region has a surface being one offlat, curved and hemispherical. The substrate may further comprise foursidewalls intersecting the first surface along four edges, and formcorners with adjacent sidewalls. A transducer is mounted at each cornerfor producing or receiving an acoustic wave, and a reflective array ismounted proximate each of the four edges. At least two transducers maybe mounted to the substrate and used to produce or receive acousticwaves. The touch sensitive region receives touch events having twocoordinates which identify a location of a touch event. First and secondtransducers may be mounted to the substrate to produce and receiveacoustic waves for detecting first and second coordinates, respectively,of the touch event on the touch sensitive region. Optionally, at leasttwo transducers may be mounted to the substrate, wherein at least one ofthe transducers is used to produce and receive acoustic waves to detecta coordinate of the touch event. Transducers are mounted to thesubstrate for producing and receiving acoustic waves over one of anentire or a portion of the touch sensitive region. In anotherembodiment, a second sidewall, formed substantially free of defects,intersects the first surface along a second edge. The second edge formsan approximate 90° angle between the second sidewall and the firstsurface, and the second edge reflects the second acoustic wave aftertraversing at least a portion of the touch sensitive region.Alternatively, one or more reflective strips are formed proximate thesecond edge and are spaced apart from each other by an integer timesone-half wavelength of the second acoustic wave. The reflective stripsand the second edge reflect the second acoustic wave after traversing atleast a portion of the touch sensitive region.

In another embodiment, a touch sensor comprises a substrate capable ofpropagating acoustic waves. The substrate includes a first surfacehaving a touch sensitive region and a first sidewall intersecting thefirst surface along a first edge. The first edge is configured topropagate a first acoustic wave along the first edge, and the firstsurface is configured to propagate a second acoustic wave across thetouch sensitive region. The second acoustic wave is based on the firstacoustic wave. A reflective array comprising partially reflectiveelements is formed on the substrate proximate the first edge for modeconversion between the first and second acoustic waves. The partiallyreflective elements may be formed by adding material to the substrate toform protrusions or removing material from the substrate to formgrooves. Alternatively, a first portion of the partially reflectiveelements may be formed by adding material to the substrate and a secondportion may be formed by removing material from the substrate. Thepartially reflective elements are formed regularly spaced with respectto each other, and may extend along at least one of the first sidewalland the first surface. Additionally, the partially reflective elementsmay have a length from the first edge of less than a wavelength of thefirst acoustic wave. A first set of regularly spaced partiallyreflective elements have a relatively strong Fourier component withrespect to a period of one wavelength of the first acoustic wave andsimultaneously a minimum Fourier component with respect to a period ofone-half wavelength of the first acoustic wave. Alternatively, thereflective array may be formed of first and second sets of regularlyspaced partially reflective elements, wherein the second set is shiftedwith respect to the first set by one-quarter wavelength of the firstacoustic wave, and the first and second sets are superposed on oneanother. The partially reflective elements may be formed having a widthalong the first edge of approximately one-half wavelength of the firstacoustic wave.

In another embodiment, a touch sensor comprises a substrate capable ofpropagating acoustic waves. The substrate includes a first surfacehaving a touch sensitive region and a first sidewall intersecting thefirst surface along a first edge. The first edge is configured topropagate a first acoustic wave along the first edge, and the firstsurface is configured to propagate a second acoustic wave across thetouch sensitive region. The second acoustic wave is based on the firstacoustic wave. The touch sensor further comprises a transducer forgenerating and receiving acoustic waves which comprises a piezoelectricelement, and a reflective array for mode conversion between the firstand second acoustic waves. The transducer may comprise a diffractivegrating positioned along the first edge, a diffractive grating formed onthe first sidewall proximate the first edge, or a diffractive gratingformed on the first surface proximate the first edge. The diffractivegrating may comprise a series of grooves being spaced apart byapproximately one wavelength of the first acoustic wave. Optionally, thediffractive grating comprises a series of grooves formed in thesubstrate which are spaced apart by approximately one wavelength of thefirst acoustic wave. Alternatively, the diffractive grating comprises aseries of grooves formed in the piezoelectric element. The piezoelectricelement may be one of a pressure-mode piezo and a shear-mode piezo. Thetransducer may further comprise a wedge element bonded to thepiezoelectric element. The wedge element is mounted on one of the firstsidewall and the first surface, and a grating is positioned on the firstedge proximate the wedge element. Alternatively, the wedge element maybe mounted on the first sidewall and form an acute angle with respect toa plane parallel to the first surface, and a grating comprisingregularly spaced grooves in the substrate is formed on the first edgeproximate the wedge element. Optionally, an angled recess may be formedby removing material from the substrate, and wedge element, bonded tothe piezoelectric element, is mounted within the angled recess. Inanother embodiment, the transducer is mounted on a second sidewall whichintersects the first surface along a second edge, the second sidewallforming a plane perpendicular to the propagation direction of the firstacoustic wave. The piezoelectric element of the transducer mounted onthe second sidewall may be a shear-mode piezo. Optionally, theshear-mode piezo may have a poling direction of approximately 45° withrespect to the touch surface. In another embodiment, the piezoelectricelement further comprises front and back sides. First and secondelectrodes may be applied to cover one of a portion and substantiallyall of the front and back sides of the piezoelectric element, forming anactive region corresponding to an area of the piezoelectric elementwhere the first and second electrodes overlap. Alternatively, thetransducer is bonded to the substrate wherein the bonding corresponds toa portion of the active region and provides strong acoustic coupling tothe substrate and the transducer in an area less than one-wavelengthsquared of the first acoustic wave. Optionally, the first electrode isapplied to cover at least a portion of the front side and a secondelectrode is applied to cover at least a portion of the front and backsides, wherein first and second electrodes on the front side receiveattachments to first and second electrical connections for exciting thepiezoelectric element. The piezoelectric element further comprises asecond edge intersecting each of the front and back sides. The secondedge is adjacent to the first edge and occupies a plane perpendicular tothe first edge. One of the front and back sides is formed to mount tothe substrate and the piezoelectric element is poled in a directionperpendicular to a plane parallel to the front and back sides. First andsecond electrodes are formed on the first and second edges, and thefirst and second electrodes receive attachments to first and secondelectrical contacts for exciting the piezoelectric element. In anotherembodiment, the piezoelectric element is mounted to the substrate havinga portion of the piezoelectric element extend beyond at least one of thefirst surface and the sidewall. Alternatively, the portion of thepiezoelectric element extending beyond at least one of the first surfaceand the sidewall extends a distance of less than one wavelength of thefirst acoustic wave.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofcertain embodiments of the present invention, will be better understoodwhen read in conjunction with the appended drawings. It should beunderstood that the present invention is not limited to the arrangementsand instrumentality shown in the attached drawings.

FIG. 1 illustrates the operation of a conventional acoustic touchsensor, an acoustic touchscreen.

FIG. 2 illustrates a touch sensor substrate having a touch surface andsidewalls in accordance with an embodiment of the present invention.

FIG. 3 illustrates partially reflective arrays formed to perturb edgewaves propagating along the edges in accordance with an embodiment ofthe present invention.

FIG. 4 illustrates an expanded view of a subset of the reflectorelements in FIG. 3 in accordance with an embodiment of the presentinvention.

FIG. 5 illustrates an alternative expanded view of the subset ofreflector elements in FIG. 3 in accordance with an embodiment of thepresent invention.

FIG. 6 illustrates the reflector elements formed on the touch surface inaccordance with an embodiment of the present invention.

FIG. 7 illustrates a touch screen having regularly spaced reflectorelements in accordance with an embodiment of the present invention.

FIG. 8 illustrates a reflector array design which minimizes backreflection of an edge wave in accordance with an embodiment of thepresent invention.

FIG. 9 illustrates a grating comprising a series of periodically spacedgrooves formed along the edge of the substrate in accordance with anembodiment of the present invention.

FIG. 10 illustrates an expanded view of the grating in accordance withan embodiment of the present invention.

FIG. 11 illustrates a piezoelectric element having wrap-aroundelectrodes that can be used in combination with a diffractive grating tocomprise a transducer in accordance with an embodiment of the presentinvention.

FIG. 12 illustrates an alternating electrical signal being applied tothe first and second electrodes of FIG. 11 in accordance with anembodiment of the present invention.

FIG. 13 illustrates the piezo bonded to the sidewalls of the substratein accordance with an embodiment of the present invention.

FIG. 14 illustrates an edge wave transducer comprising the piezo bondedover the grating in the sidewall of the substrate in accordance with anembodiment of the present invention.

FIG. 15 illustrates an edge wave transducer design incorporating ashear-mode piezoelectric element (shear-mode piezo) in accordance withan embodiment of the present invention.

FIG. 16 illustrates an alternative piezo in accordance with anembodiment of the present invention.

FIG. 17 illustrates a piezo having front and back electrodes on oppositesides of the piezoelectric element in accordance with an embodiment ofthe present invention.

FIG. 18 illustrates an alternative piezo in accordance with anembodiment of the present invention.

FIG. 19 illustrates a wedge transducer assembly mounted to the sidewallof the substrate in accordance with an embodiment of the presentinvention.

FIG. 20 illustrates the wedge transducer assembly being tilted withrespect to the edge in accordance with an embodiment of the presentinvention.

FIG. 21 illustrates a wedge transducer assembly mounted to the substratein accordance with an embodiment of the present invention.

FIG. 22 illustrates an alternative piezo in accordance with anembodiment of the present invention.

FIG. 23 illustrates the piezo mounted to the substrate in accordancewith an embodiment of the present invention.

FIG. 24 illustrates an edge wave touch sensor system formed inaccordance with an embodiment of the present invention.

FIG. 25 illustrates a touch panel in accordance with in embodiment ofthe present invention.

FIG. 26 illustrates a touch panel in accordance with an embodiment ofthe present invention.

FIG. 27 illustrates a large touch panel comprising four piezos inaccordance with an embodiment of the present invention.

FIG. 28 illustrates a block diagram of a touch monitor interconnectedwith a computer in accordance with an embodiment of the presentinvention.

FIG. 29 illustrates an example of a round table top in accordance withan embodiment of the present invention.

FIG. 30 illustrates an edge-wave packet propagating along an approximate90° edge of the substrate in accordance with an embodiment of thepresent invention.

FIG. 31 illustrates an alternative edge wave touch sensor system formedin accordance with an embodiment of the present invention.

FIG. 32 illustrates a touch sensor wherein a single transmit transducergenerates X and Y signals in accordance with an embodiment of thepresent invention.

FIG. 33 illustrates an alternative touch sensor wherein a singletransmit transducer generates X and Y signals in accordance with anembodiment of the present invention.

FIG. 34 illustrates a geometry of the substrate near the common transmittransducer in accordance with an embodiment of the present invention.

FIG. 35 illustrates an alternative geometrical option in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Conventional reflective arrays 13 a-13 d as shown in FIG. 1 range inwidth between about 5 mm and 15 mm, which corresponds to a range ofabout 9-26 acoustic wavelengths (assuming a conventional frequency ofabout 5 MHz, corresponding to a wavelength of about 0.57 mm). Thereflective arrays having narrower widths are typically used on smallerscreens.

Acoustic surface waves concentrate acoustic energy near atwo-dimensional surface. The surface can be described as guiding thewaves, as the acoustic surface waves propagate near the surface withoutdiffusing away from the surface if the surface is flat or even if thesurface has a slight curvature. One-dimensional edge acoustic waves area type of acoustic wave. One-dimensional edge acoustic waves may bereferred to as edge waves, flexural edge waves, or line acoustic waves.The wave energy of edge waves is localized about an edge of a surfaceand decays approximately exponentially in the directions normal to theedge. Therefore, the energy vector propagates along the edge. Edge wavesare non-dispersive; their velocity is independent of frequency. Usingnon-dispersive waves in touch sensors is advantageous becausepropagation of acoustic waves will not distort touch-inducedperturbations of received signals from their simple dip shape into morecomplex oscillatory shapes.

The majority of an edge wave's energy is within one wavelength of anapproximate 90° corner defining the edge. Because of the exponentialfalloff in energy away from the edge, essentially no energy is foundbeyond two wavelengths of the edge. For edge waves having a frequency ofabout 5 MHz in glass, this means that an edge wave is confined to withinabout 1 mm of the edge. For a 2 mm thick glass plate, edge waves maypropagate along the top edge of a sidewall without being affected by thepresence of the bottom edge of the sidewall only 2 mm away. As the edgewave energy is confined to about 1 mm of the edge, it is possible tomake a touch sensor with very narrow functional borders using edge wavetechnology. Therefore, a housing for a touch sensor incorporating edgewaves can have a very narrow bezel region, and the touch sensitive areaof the touch sensor can be increased.

FIG. 2 illustrates a touch sensor substrate 20 having a touch surface 24and sidewalls 32 in accordance with an embodiment of the presentinvention. Any suitable material can be used for the substrate 20,including glass, ceramic, and metals (e.g., aluminum or steel). For someapplications, low acoustic loss glass may be desired. For example,borosilicate glasses have low loss, and can provide increased receivedsignal amplitudes that may in turn enable larger touch sensor areas.

Clean edges 22 are formed on the substrate 20 at an intersection betweena plane corresponding to the touch surface 24 and planes correspondingto each of the sidewalls 32. The clean edges 22 are formed to besubstantially free of defects, such that any deviations on the cleanedge 22 such as chips, striations, dents, uneven regions, and the likehave dimensions less than the acoustic wavelength. For a givenfrequency, the edge-wave wavelength is only a few percent shorter thanthe wavelength of the much better known Rayleigh wave. Therefore, makinguse of the Rayleigh wavelength as a well known and defined measurement,it may be noted that defects are preferably less than 20% of a Rayleighwavelength.

The clean edges 22 may be formed by any method suitable for the materialfrom which the substrate 20 is manufactured. For example, glass may becut and machined to provide clean edges 22. Alternatively, the cleanedge 22 may be formed by propagating a controlled fracture using thermalstress, for example by utilizing localized laser heating and gas jetcooling processes. Optionally, the glass may be scribed and brokenwhich, if carefully done, can produce a clean edge 22 opposite thescribed surface.

Angles 42 and 44 formed where the sidewalls 32 abut the touch surface 24are 90°, or within 20° of 90°, making sidewalls 32 vertical orsubstantially vertical with respect to the touch surface 24. By way ofexample only, for an edge 22 having an angle 42 or 44 much less than90°, multiple edge wave modes with differing velocities can exist.However, if the edge 22 has an angle 42 or 44 within +/−10° of 90°, theedge 22 will support only a single edge wave mode. This is desirable asit eliminates the possibility of mode mixing as an edge wave propagatesalong the edge 22.

Opposing edges 26 are formed on the substrate 20 at an intersectionbetween a plane corresponding to a second surface 28 of the substrate 20and the planes corresponding to each of the sidewalls 32. The opposingedges 26 do not have to be clean, unless it is desired to also utilizethe second surface 28 as a touch surface. If only one touch surface isdesired, manufacturing time or cost can be minimized by only having toform clean edges adjacent to one surface.

FIG. 30 illustrates an edge-wave packet 580 propagating along anapproximate 90° edge 22 of the substrate 20 in accordance with anembodiment of the present invention. The edge wave propagates in the Xdirection, as indicated in FIG. 30. The dominant component of materialmotion (i.e. motion of atoms within the substrate 20) as the edge wavepasses is perpendicular to the propagation direction X and at 45° withrespect to both the Y and Z directions. Material deflections have beenexaggerated in FIG. 30 for clarity. Note that the vast majority of theenergy in the edge-wave packet 580 is contained within an edge-wavewavelength distance from the 90° edge 22 along the touch surface 24 andthe sidewall 32.

FIG. 3 illustrates partially reflective arrays 30 formed to perturb edgewaves propagating along the edges 22 in accordance with an embodiment ofthe present invention. Transducers (not shown) are used to convertbetween electrical signals and acoustic waves and will be discussedfurther below. For touch sensor systems, generally, electrical signalswill be transmitted between a controller and a transducer to generateand/or receive acoustic signals.

The reflective arrays 30 comprise reflector elements 34 spaced proximatethe clean edges 22 to perturb the edge waves propagating along the edges22. A first wave, the one-dimensional edge wave, is generated andpropagated along the edges 22 and within one wavelength of the edges 22.The reflective arrays 30 can be used to convert the edge waves to secondacoustic waves, or two-dimensional surface acoustic waves (SAW),propagating across the touch surface 24 of the substrate 20. Thereflective arrays 30 are reversible, and therefore can also be used toconvert the second acoustic wave to a third acoustic wave, or aone-dimensional edge wave. The second acoustic wave can be any type ofwave that will provide sufficient touch sensitivity over atwo-dimensional touch surface, including surface bound waves likeRayleigh waves (where the term is meant to include quasi-Rayleigh waves)and plate waves (e.g., Lamb and shear waves). The reflector elements 34in FIG. 3 are regularly (periodically) spaced apart along edges 22, andmay extend along the sidewalls 32 of the substrate 20 along the Y axis(as shown in FIG. 3) and/or extend into the horizontal touch surface 24.As discussed below, the reflector elements 34 may be formed by eitherdepositing material or removing a portion of the substrate 20.

As an edge wave travels along the edge 22 and encounters each of thereflector elements 34, the edge wave is partially transmitted to reachthe next reflector element 34, partially absorbed or scattered by thereflector element 34, and partially converted by the reflector element34 to Rayleigh waves bound to the surface 24 through 90° scattering andmode conversion between the one-dimensional edge wave and thetwo-dimensional Rayleigh surface acoustic wave (SAW).

FIG. 4 illustrates an expanded view of a subset 36 of the reflectorelements 34 in FIG. 3 in accordance with an embodiment of the presentinvention. The reflector elements 34 are illustrated as protrudingreflector elements 86. The reflector elements 86 are periodically spacedapart by a distance 48 of approximately a wavelength of the edge waves(λ_(E)) traveling along the edge 22. Therefore, the surface Rayleighwaves launched by the mode conversion by the reflector elements 86 willbe synchronous with each other. Many possible shapes are possible forreflector elements 86. As one specific example, the reflector elements86 may be rectangular in shape, having a width 40 along the X axis ofapproximately λ_(E)/2, a height 38 along the Y axis of approximatelyλ_(E) or less, and a depth 46 along the Z axis of much less than λ_(E),such as less than a few percent of λ_(E). By way of example, the depth46 dimension of the reflector elements 86 extends outward from an outersurface of the sidewall 32 along the Z axis. A top edge 80 of thereflector elements 86 may be formed flush with the edge 22 or within adistance 82 of the edge 22.

The reflector elements 86 may be made of any suitable material. Forexample, fired on ceramics (e.g., glass frit) can be used.Alternatively, the reflector elements 86 may comprise a loaded-polymerUV-curable ink such as disclosed in U.S. Pat. No. 5,883,457, which isincorporated herein by reference. One example of a useful loaded-polymerUV-curable ink is one that is loaded with inorganic particles, and yetis soft compared to the substrate 20 due to its polymer matrix.Reflector elements 86 comprising such loaded polymer inks will induceonly minor stiffness perturbations and will couple dominantly via massloading or inertial effects. Therefore, reflector elements 86 may befabricated that are mainly mass loading in nature. Reflector elements 86may be formed on the substrate 20 by any suitable method, such asdepositing by screen printing, pad printing, ink jet processes,micro-dispensing, and the like.

FIG. 5 illustrates an alternative expanded view of the subset 36 ofreflector elements 34 in FIG. 3 in accordance with an embodiment of thepresent invention. In FIG. 5, the reflector elements 34 are illustratedas grooved reflector elements 88. The reflector elements 88 may beformed by removing small regions of the substrate 20 along the sidewalls32 to form grooves or notches. As illustrated previously, the reflectorelements 88 are periodically spaced apart by a distance 48 ofapproximately a wavelength of the edge wave (λ_(E)) traveling along theedge 22. Reflector elements 88 can have any of a wide variety of shapes,for example, the reflector elements 88 may be rectangular in shape,having a width 40 along the X axis of approximately λ_(E)/2, a height 38along the Y axis of approximately λ_(E) or less, and a depth 84 alongthe Z axis of much less than λ_(E), such as less than a few percent ofλ_(E). The depth 84 dimension of the reflector elements 88 extendsinward from the outer surface of the sidewall 32 along the Z axis.

Compared to protruding reflector elements 86 formed of material such asUV-curable inks as discussed with FIG. 4 which induce only minorstiffness perturbations and couple dominantly via mass loading orinertial effects, grooved reflector elements 88 couple to edge wavesmore as perturbations in substrate stiffness. Reflector elements 88 canbe back-filled with other materials, such as a soft, loaded polymer, forexample, to tune the mass-loading and stiffness-perturbationcharacteristics of the reflector elements 88.

FIG. 6 illustrates the reflector elements 34 formed on the touch surface24 in accordance with an embodiment of the present invention. Thereflector elements 34 are periodically spaced apart by the distance 48of approximately a wavelength of the edge waves (λ_(E)) traveling alongthe edge 22. The reflector elements 34 have the width 40 along the Xaxis of approximately λ_(E)/2, the height 38 along the Z axis ofapproximately λ_(E) or less, and a depth (not shown) along the Y axis.As discussed previously, the depth dimension may extend outward from anouter surface of the touch surface 24 if the reflector elements 34 areformed of additional material, or extend inward from the outer surfaceof the touch surface 24 if the reflector elements 34 are formed byremoving material from the substrate 20. Optionally, reflector elements34 may be formed on both the touch surface 24 and sidewalls 32 such asby combining the reflector elements 34 of FIG. 3 with the reflectorelements 34 of FIG. 6.

As edge wave power density is very close to zero when more than awavelength away from the edge 22, structures more than one wavelengthaway will have essentially no coupling to the edge wave. In contrast,any perturbation of the edge 22 and any perturbation within onewavelength of the edge 22 on the touch surface 24 or the sidewalls 32will scatter edge wave energy. Therefore, by varying the nature (massloading, stiffness perturbation, etc.), geometry and location of thereflector elements 34, the relative strengths of coupling between theedge wave and various other acoustic modes (Rayleigh waves, Lamb waves,shear waves, etc.) can be tuned.

Coupling between edge waves and Rayleigh waves is of interest. Hightouch sensitivity and lack of dispersion make Rayleigh waves attractiveas a touch sensing acoustic mode. Furthermore, the depth profiles ofRayleigh waves and edge waves are very similar thus making strong andpreferential coupling to Rayleigh waves easier than edge wave couplingto other modes. Numerical simulations may be used to optimize theperturbation design to optimize edge wave coupling to Rayleigh waves orto an alternate touch-sensitive acoustic mode.

The desired nature of the reflector elements 34 depends in part on thedesired touch-sensing acoustic mode. Each individual reflector element34 is intended to reflect only a small portion of the incident edge waveenergy, and therefore in the case of the grooved reflector elements 88of FIG. 5, the depth 84 into the substrate 20 is generally much lessthan λ_(E), e.g., of order of a percent of a wavelength or a fewmicrons, and can be adjusted to achieve desired tradeoffs betweenacoustic loss and conversion efficiency between the one-dimensional edgewaves and the two-dimensional surface acoustic waves.

The reflective arrays 30 can be designed to couple edge waves toRayleigh waves that propagate across the touch surface 24 at a diagonalangle, rather than perpendicular to the edge 22. The distance 48 betweenthe reflector elements 34 can be adjusted to tune the reflective angle.If s represents the distance 48 and θ is the angle of the Rayleigh wavepropagation direction with respect to normal to the edge 22, thecondition for coherent scattering at angle θ is:

s sin(θ)=s(λ_(R)/λ_(E))−n λ_(R),

where n is an integer, λ_(R) represents the wavelength of the Rayleighwave, and λ_(E) represents the wavelength of the edge wave.

FIG. 7 illustrates a touch screen 128 having regularly spaced reflectorelements 34 in accordance with an embodiment of the present invention.For simplicity, reflector elements 34 are illustrated on only two of thefour edges 22, namely for the transmitting reflector element array 176and receiving reflector element array 178. It should be understood thatthe reflector elements 34 may be formed as discussed previously in FIGS.3-6. The reflector elements 34 are periodically spaced apart by thedistance 48 of approximately a wavelength of the edge wave (λ_(E))traveling along the edge 22.

Arrows 164, 174, and 166 illustrate a desired acoustic path fromtransmit transducer 162 to the receive transducer 168. Also illustratedin FIG. 7 are undesired acoustic paths leading to interfering signals atreceive transducer 168. The undesired acoustic paths are caused by 180°backscattering of edge waves by the reflector arrays 176 and 178. Thearray of regularly spaced reflector elements 34 having wavelengthspacing (distance 48) as needed for 90° scattering of SAW to edge wavesmay also lead to 180° backscattering of the edge wave.

A first edge wave is propagated by the transmit transducer 162 alongedge 22 in the direction of arrow 164. The edge wave is converted by thereflector elements 34 of the transmitting reflector element array 176 toa SAW wave traveling across the touch surface 24 in the direction ofarrow 174. Some of the edge wave power from transmit transducer 162 willcontinue propagating along the edge 22 as shown by arrow 184. Ifreflector elements 34 backscatter edge waves by 180°, an undesired edgewave will be generated in the direction of arrow 185. This undesirededge wave will also be scattered and mode converted at 90°, thuscontributing an undesired delayed contribution to the Rayleigh wave(arrow 174), eventually leading to a parasitic interfering signal atreceive transducer 168.

Furthermore, 180° edge-wave backscattering also generates undesiredparasites at the receiving reflector element array 178. The desired SAWwave (arrow 174) is converted to two edge waves by the regularly spacedreflector elements 34 of the receiving reflector element array 178.Therefore, a second edge wave traveling in the direction of arrow 166 toreceiving transducer 168 and an undesired parasitic edge wave travelingin the direction of arrow 186 are created. The parasitic edge wave maythen be backscattered by 180° back towards the receive transducer 168 bythe reflector elements 34 as illustrated by arrow 187. It is desirableto design reflector elements 34 in such a manner to minimize the 180°edge-wave backscattering in order to minimize the amplitudes of theparasitic paths shown in FIG. 7.

FIG. 8 illustrates a reflector array design 150 which minimizes backreflection of an edge wave in accordance with an embodiment of thepresent invention. Such designs are applicable to both transmit andreceive arrays such as items 176 and 178 of FIG. 7. First and secondreflector elements 152 and 154 are illustrated on the touch surface 24of the substrate 20, but it should be understood that the first andsecond reflector elements 152 and 154 may be formed on the sidewalls 32in addition to, or instead of, the touch surface 24. In addition, thefirst and second reflector elements 152 and 154 may be formed as groovesor protrusions. The first reflector elements 152 are spaced 1 wavelengthof the edge wave apart with respect to each other. The second reflectorelements 154 are shifted with respect to the first reflector elements152 by a distance 182 substantially equivalent to one-quarter wavelengthof the edge wave. First and second reflector elements 152 and 154 have awidth 180 of less than one-quarter wavelength, equal to one-quarterwavelength, or larger than one-quarter wavelength, in which casereflector elements 152 and 154 are overlapping or superposed.

In other words, the reflector array design 150 may be created by firstdesigning the first reflector elements 152 without regard to the need tosuppress 180° back reflection of edge waves. The first reflectorelements 152 are then shifted by one-quarter wavelength (in eitherdirection) to create the second reflector elements 154. The secondreflector elements 154 are then superposed on the first reflectorelements 152.

When an edge wave is propagated along the edge 22 in the direction ofarrow 156, a SAW wave 158 and a reflected wave 170 are created by thefirst reflector 152. A SAW wave 160 and a reflected wave 172 are createdby the second reflector 154. Therefore, two SAW waves are created at 90°and 2 reflected edge waves are created at 180° with respect to thedirection of propagation of the edge wave.

The reflected waves 170 and 172 have an extra one-half wavelength pathand hence a relative phase shift of 180° which substantially cancels orminimizes the 180° back reflection. There is a delay of one-quarterwavelength between the SAW waves 158 and 160 which creates only a 90°phase shift between the two waves which does not lead to cancellation ofthe scattering amplitude. In other words, if the distance betweenadjacent first and second reflective elements 152 and 154 along the edge22 alternates between one-quarter and three-quarters wavelengths, then180° backscattering will be suppressed while 90° edge-SAW coupling willnot be suppressed.

By way of example only, let the coordinate x represent distance alongedge 22 shown in FIG. 8. Let P(x) represent the periodic variation ofthe scattering strength of reflectors 152. P(x) can be Fourier expandedinto the form P(x)=ΣPn*exp(i(2πn/λ)x). Below, the condition for minimal180° back reflection in terms of the Fourier coefficients Pn isconsidered. (This discussion can be generalized to the case that thestrength of the reflectors 152 gradually increases with distance fromthe transducer as is often desired for signal equalization. In thiscase, let r(x) be a slowly varying reflector strength weighting as afunction of x, and also let R(x)=r(x)*P(x) where P(x) is a periodicfunction P(x)=P(x+λ) that describes the detailed shape of each groove.)

The scattering of SAW to edge waves at 90° (in direction of arrows 158and 160) is due to the n=±1 terms in the Fourier series of the grooveshape while the 180° backscattering of edge waves (in the direction ofarrows 170 and 172) is due to the n=±2 terms of the Fourier series. Theundesirable backscattering of the edge waves in the direction of arrows170 and 172 can be eliminated if the n=±2 terms in the Fourier seriesare eliminated.

One way to eliminate the n=±2 terms in the Fourier series is to startwith an arbitrary periodic function P(x) with non-zero fundamental n=±1components that couple SAW and edge waves as desired, shift the patternby one-quarter wavelength and superpose this on the original patternP(x)→P′(x)={P(x)+P(x+λ/4)} or in terms of the Fourier componentsPn→P′n=(1+i^(n))Pn so that P′n=0 for n=±2 but not n=±1.

Referring to FIGS. 4 and 5, the reflector elements 86 and 88 areone-half wavelength wide and spaced 1 wavelength apart. This correspondsto a case of FIG. 8 wherein the first and second reflector elements 152and 154 are each one-quarter wavelength wide and spaced 1 wavelengthapart. When the first reflector elements 152 are replicated, shifted byone-quarter wavelength and superposed, the result is a series ofreflector elements 86 or 88 having a width 40 of one-half wavelength andbeing positioned apart the distance 48 of one wavelength.

A transducer may be used to convert electrical signals to acoustic edgewaves that propagate along the edge 22. One example of a transducerassembly is a piezoelectric element in combination with a gratingelement, where the grating element is disposed between the piezoelectricelement and the medium, such as substrate 20, in which the generatedacoustic mode is to propagate. The grating acts as a diffractive elementthat couples acoustic energy from the transducer to acoustic waves onthe substrate 20.

FIG. 9 illustrates a grating 50 comprising a series of periodicallyspaced grooves 52 formed along the edge 22 of the substrate 20 inaccordance with an embodiment of the present invention. The grooves 52can be formed in the substrate 20 using any suitable manufacturingmethod, for example, machining, etching, laser ablation, grinding,patterning, molding, and the like.

FIG. 10 illustrates an expanded view of the grating 50 in accordancewith an embodiment of the present invention. A height 54 along the Yaxis of the grooves 52 is approximately equal to or less than awavelength of the edge wave λ_(E). A depth 58 of the grooves 52 alongthe Z axis is approximately equal to or much less than the wavelength ofthe edge wave λ_(E). The grooves 52 are spaced apart by a distance 74which is approximately equal to the wavelength of the edge wave λ_(E).The width 56 of the grooves 52 along the X axis is approximatelyone-half the wavelength of the edge wave, or λ_(E)/2. The design of thegrating 50 has much in common with the design of reflector arrayscomprising grooved reflector elements 88 as shown in FIG. 5 as bothserve a similar function of coherently coupling to edge waves. The majordifference is in the strength of the coupling. For efficient transducerdesign, the grating 50 must excite or extract much of the energy of anedge wave in the short length of grating 50 while reflector arrays 30 inFIG. 3 spread out the coupling between edge waves and Rayleigh wavesacross most of the lengths of the edges 22. As a result, the depth 58 ingrating 50 is typically significantly deeper than depth 84 in FIG. 5.

FIG. 11 illustrates a piezoelectric element 90 having wrap-aroundelectrodes that can be used in combination with a diffractive grating tocomprise a transducer in accordance with an embodiment of the presentinvention. A first electrode 64 is present on a lower region 65 of afront side 66 of the piezoelectric element 90 and wraps around a bottomside 76 of the piezoelectric element 90 to a back side 70 of thepiezoelectric element 90. A second electrode 72 is present on an upperregion 73 of the front side 66 of the piezoelectric element 90. Thefirst and second electrodes 64 and 72 may be comprised of silver frit,printed nickel, or any other conductive material.

The assembly comprising the piezoelectric element 90 and electrodes 64and 72 is often referred to as a piezo 60. The piezoelectric element 90is a pressure mode piezoelectric element. PZT (a lead-zirconium-titanateceramic) is a common material used to fabricate piezoelectric elements,but other piezoelectric materials such as polymer PVDF (polyvinylidenefluoride) and lead-free ceramics may also be used. The height of theactive region of the piezo 60 is matched to the vertical profile of theedge wave, i.e., approximately equal to λ_(E) or less. The active regionof the piezo 60 is determined by the geometry of the electrode 72 asonly the piezoelectric material sandwiched between electrodes 72 and 64is mechanically excited when a voltage is applied to the electrodes 72and 64. For handling ease, it is convenient that the piezo dimension 62can extend beyond the active region and hence is allowed to be muchlarger than the edge wave wavelength λ_(E).

FIG. 12 illustrates an alternating electrical signal 96 being applied tothe first and second electrodes 64 and 72 of FIG. 11 in accordance withan embodiment of the present invention. The geometry of the wrap-aroundfirst electrode 64 and the second electrode 72 causes only the upperregion 73 of the piezo 60 to be electrically active.

Piezoelectric elements 90 typically have a thickness 78 corresponding toone-half wavelength of acoustic waves in the piezoelectric material atthe operating frequency. (For clarity, the thickness of electrodes 64and 72 are exaggerated in FIG. 12.) For a pressure-mode piezo 60operated at about 5 MHz, the thickness 78 is typically about 400 μm.Electrical connection to the first and second electrodes 64 and 72 canbe made using any suitable method, for example, by spring contacts,solder, conductive epoxy (e.g., silver loaded), or a conductive adhesivewith directional conductivity (e.g., a Z-axis adhesive havingsignificant conductivity only perpendicular to the plane of theelectrodes 64 and 72). Attributes to consider when determiningconnection methods include a low resistance junction, lowelectromagnetic interference and susceptibility, high reliability, lowcost and the like.

FIG. 13 illustrates the piezo 60 bonded to the sidewalls 32 of thesubstrate 20 in accordance with an embodiment of the present invention.Four piezos 60 are bonded in four different locations along the fourdifferent edges 22.

FIG. 14 illustrates an edge wave transducer 98 comprising the piezo 60bonded over the grating 50 in the sidewall 32 of the substrate 20 inaccordance with an embodiment of the present invention. As shown inFIGS. 13 and 14, the piezos 60 are bonded over the grooves 52 in thegrating 50, with the electrically active upper region 73 overlapping thegrooves 52. An adhesive can be used to bond the piezo 60 over thegrating 50 such that the adhesive fills or partially fills the grooves52. The mechanical properties of the adhesive can be chosen so that themotions of the piezo 60 are largely decoupled from the sidewall 32 ofthe substrate 20 in the region of the grooves 52. Alternatively, thegrating 50 may be designed to provide strong acoustic coupling betweenthe piezo 60 and the grooves 52. In some applications, it may be desiredto choose the adhesive in the grooves 52 to slow the speed of thepressure waves traveling from the piezo 60 to the substrate 20 at thebottom of the grooves 52 so that piezo vibration coupling to the edgewaves within the grooves 52 is phase shifted by approximately 180° withrespect to coupling between the grooves 52. In this manner, coupling topiezo vibrations within the grooves 52 adds coherently to couplingbetween the grooves 52 to generate edge waves.

Alternatively, a grating (not shown) can be formed on a side of thepiezo 60 instead of on the sidewall 32 of the substrate 20 so that nograting 50 need be fabricated in substrate 20. The grating side of thepiezo 60 can then be bonded to the substrate 20 to provide the couplingmechanism between acoustic waves generated by the piezo 60 and an edgewave. Furthermore, as the edge wave is symmetric between the twosurfaces forming the edge, such as the edges 22 formed by theintersection of the touch surface 24 and sidewalls 32, edge wavetransducer 98 may instead be mounted to the touch surface 24 of thesubstrate 20. Alternatively, edge wave transducer 98 may be formed onboth the sidewalls 32 and touch surface 24.

FIG. 15 illustrates an edge wave transducer design 100 incorporating ashear-mode piezoelectric element (shear-mode piezo) 120 in accordancewith an embodiment of the present invention. The shear-mode piezo 120comprises a piezoelectric material 118 having front side 138, back side184, and first, second, third and fourth sides 188-194. A firstelectrode 122 is present on a triangular shaped region 136 on the frontside 138 of the piezoelectric material 118. The second electrode 124 ispresent on a bottom triangular region 196 on the front side 138 of thepiezoelectric material 118 and wraps around the bottom side 148 to theback side 184 of the piezoelectric material 118.

The shear-mode piezo 120 is bonded to the sidewall 32 of the substrate20 and abuts the touch surface 24. The shear-mode piezo 120 iselectrically active in the upper left hand corner corresponding to theregion 136 and generates motion with polarization or a component ofpolarization at approximately a 45° angle with respect to the X and Yaxes as indicated by double arrow 127. The shear motion of theshear-mode piezo 120 then couples to an edge wave propagating in the Zdirection as indicated by arrow 126. Note that the shear-mode piezo 120directly excites the edge wave; there is no need for a grating structuresuch as item 50.

FIG. 16 illustrates an alternative piezo 200 in accordance with anembodiment of the present invention. A front electrode 204 is present ona upper region 206 of a front side 208 of a piezoelectric element 202. Aback electrode 210 is present on a lower region 212 on the front side208 of the piezoelectric element 202 and wraps around a bottom side 214to a back side 216 of the piezoelectric element 202. The back electrode210 extends along the back side 216 to cover the upper region 206 of thepiezoelectric element 202 only in an active region 218.

A first electrical connection 220 is interconnected with the frontelectrode 204 by soldering, wire-bonding, or other interconnectionmethods. A second electrical connection 222 is interconnected with theback electrode 210. The size of the piezo 200 is larger than the activeregion 218 to allow room to connect the first and second electricalconnections 220 and 222 to the front and back electrodes 204 and 210 forease of manufacturing, while limiting the size and shape of the activearea 218 to prevent scattering too much energy. Opposite polarities areapplied to the front and back electrodes 204 and 210. The size of theactive area 218 is, by way of example only, of order of one-tenth of asquare edge-wave wavelength, i.e. ≈0.1*λ_(E) ². As wavelength variesinversely with operating frequency, the active area 218 tends todecrease if the piezo 200 is designed for a higher operating frequency.FIG. 16 illustrates an example where the active area 218 is square inshape. Other shapes for the active area 218 are possible withappropriate shaping of electrodes 204 and 210 to produce the desiredoverlap geometry.

The piezos in FIGS. 15 and 16 limit excitation of the substrate 20 to asmall region corresponding to the cross sectional area of a propagatingedge wave. In these piezos, piezoelectric excitation is limited to thedesired edge-wave cross-sectional area. An alternate approach is topiezoelectrically excite a larger piezo area, such as create a largeractive area 218, but limit mechanical coupling between the piezo 200 andthe substrate 20 to the small cross-sectional area of the propagatingedge wave.

FIG. 17 illustrates a piezo 224 having front and back electrodes 226 and228 on opposite sides of piezoelectric element 246 in accordance with anembodiment of the present invention. A front electrode 226 and a backelectrode 228 substantially cover a front side 254 and back side 256,respectively, of a piezoelectric element 246. As in the piezos of FIGS.15 and 16, the piezo 224 is poled to produce a shear-mode piezo withshear motion in a 45° direction. When such a piezo 224 is bonded to acorner of the substrate 20, a stiff adhesive such as epoxy may be usedin the desired active area to accomplish strong mechanical coupling tothe substrate 20 while an air gap or a weak shear coupling material suchas silicone rubber (RTV) can be used elsewhere. If it is desirable tomake electrical connections to both front and back electrodes 226 and228 on the same surface, a wrap around electrode may be used as shown inFIG. 18.

FIG. 18 illustrates an alternative piezo 230 similar to that shown inFIG. 17 in accordance with an embodiment of the present invention. Afront electrode 232 is present on a front side 234 of a piezoelectricelement 236. A back electrode 238 is present on a corner region 240 onthe front side 234 of the piezoelectric element 236 and wraps around aportion of a side 242 to a back side 244 of the piezoelectric element236. The back electrode 238 extends along the back side 244 to cover thepiezoelectric element 236, forming an active region where the frontelectrode 232 and back electrode 238 overlap. In the alternative piezo230, nearly the entire area of the piezo 230 is piezoelectricallyactive. Appropriate design and fabrication of the bond between the piezo230 and the substrate 20 limit the acoustic coupling to the substrate 20to the desired region for edge-wave generation and reception.

FIG. 19 illustrates a wedge transducer assembly 130 mounted to thesidewall 32 of the substrate 20 in accordance with an embodiment of thepresent invention. A piezoelectric element 250 is mounted to one side ofa wedge 252. An opposing side of the wedge 252 is mounted to thesidewall 32 of the substrate 20. The tilt of piezo element 250 withrespect to the vertical surface of sidewall 32 defines an angle 248 ofthe wedge 252. This wedge angle 248 is controlled so that bulk pressurewaves excited by the piezo 250 and propagating in the wedge 252 cancouple to vertically propagating Rayleigh waves on sidewall 32 ofsubstrate 20.

When excited, the piezoelectric element 250 launches a bulk wave in thewedge 252. A surface acoustic Rayleigh wave (SAW) is launched andpropagates along the sidewall 32 as indicated by arrow 132; thereforepropagating perpendicular to edge 22 in FIG. 19. The Rayleigh wave inturn interacts with the grating 50 which comprises grating elements 52.As described above, the grating elements 52 have a height 54 in the Yaxis direction approximately equal to or less than the wavelength of anedge wave λ_(E) and are spaced apart by approximately λ_(E). The width56 of the grating elements 52 is approximately λ_(E)/2. The grating 50can couple two-dimensional surface waves (the Rayleigh waves) to aone-dimensional edge wave, thereby launching an edge wave as indicatedby arrow 134 along the edge 22.

The transducer design of FIG. 19 may lead to a parasitic SAW pathbetween transmit/receive pairs of wedge transducer assemblies 130. Forexample, parasitic components of the first SAW launched by the wedgetransducer assembly 130 can propagate up the sidewall 32, across thesensor surface 24, and down the opposite sidewall 32 to a receivingwedge transducer placed on the opposite sidewall 32. This parasitic pathcan be interrupted by tilting the wedge transducer assembly 130 withrespect to the edge 22.

FIG. 20 illustrates the wedge transducer assembly 130 being tilted withrespect to the edge 22 in accordance with an embodiment of the presentinvention. Therefore, the angle of intersection between the Rayleighwave launched by the wedge transducer assembly 130 and the edge 22 isdifferent than 90°. The spacing s between the grooves 52 of the grating50 for coupling between a SAW launched at an angle φ is given by thefollowing relation:

1=s/λ _(E) +s*sin (φ)/λ_(R).

FIG. 21 illustrates a wedge transducer assembly 130 mounted to thesubstrate 20 in accordance with an embodiment of the present invention.A portion of the substrate 20 of the opposing surface 28 opposite thetouch surface 24 can be removed to form an angled recess 140 at a cornerproximate intersecting planes formed by two of the sidewalls 32. Thewedge transducer assembly 130 including the wedge 142 and thepiezoelectric element 144 can be mounted in the recess 140. Therefore,wedge transducer assembly 130 does not protrude beyond the planes of thesidewalls 32 or substrate surfaces 24 and 26.

FIG. 22 illustrates an alternative piezo 260 in accordance with anembodiment of the present invention. The piezo 260 comprises apiezoelectric element 262 having a notched corner 264. The notchedcorner 264 may be formed having an angle 266 of approximately 45° withrespect to planes formed by first and second edges 268 and 270 of thepiezoelectric element 262.

By way of example only, for 5.5 MHz operation, the piezoelectric element262 may be approximately 200 microns in depth 272 along the Z axis. Moregenerally, depth 272 is chosen so that there is a shear-mode resonanceat the operating frequency, that is, depth 272 is approximately equal toone-half of a bulk shear wave wavelength in the material ofpiezoelectric element 262. The width 274 and height 276 along the X axisand Y axis, respectively, of the piezoelectric element 262 may each be 2mm. First and second electrodes 278 and 280 may be formed on the firstand second sides 268 and 270, respectively. Poling is accomplished alongthe Z axis.

FIG. 23 illustrates the piezo 260 mounted to the substrate 20 inaccordance with an embodiment of the present invention. Mounting issimilar to that shown in FIG. 15 for the shear-mode piezo 120. The piezo260 may be mounted to the substrate 20 having the notched corner 264mounted flush with edge 22 as shown in FIG. 23. Alternatively piezosides 268 and 270 may be flush with surfaces of substrate 20.

By mounting the piezo 260 such that the piezo sides 268 and 270 form anoverhang beyond the touch surface 24 and sidewall 32, greater efficiencymay be achieved. The amount of overhang, or the distance the piezo sides268 and 270 extend beyond the touch surface 24 and sidewall 32, may beequal to or less than an edge-wave wavelength. The overhang design maybe applied equally to transducers based on the piezo design of FIGS. 15,16 and 18, as well as the transducer design of FIG. 14.

Returning to FIG. 22, wires 282 and 284 may be attached to the first andsecond electrodes 278 and 280 as previously discussed. When excited byan alternating electrical signal 286, motion, or shear-mode oscillation,is generated within the piezoelectric element 262 as indicated by arrows288-294. The strength of the vibration is stronger within thepiezoelectric element 262 close to the notched corner 264, as indicatedby arrow 288. Moving further away from the notched corner 264, thestrength of the vibration and amplitude of the shear-wave decreases in acontrolled manner.

The basic edge-wave excitation mechanism is the same for the shear-modepiezo 120 and piezo 260 in FIGS. 15 and 23, respectively. An advantageof piezo 260 of FIGS. 22 and 23 is that by appropriate design of thenotch 264 geometry and the placement of the piezo 260 on substrate 20,the piezoelectric excitation pattern can be closely matched to the crosssectional profile of edge wave motion. This maximizes the ratio of piezocoupling to the desired edge-wave mode relative to parasitic coupling toother modes.

Because edge wave cross sections are very small, piezos, such as piezo260, are very small and have high impedance when compared to theimpedances of 50Ω of conventional transducers used to generate the SAW.As impedance is inverse with respect to the size of the active area,impedance is now into the kΩ region. Therefore, it should be understoodthat the controllers, such as the controller 112 in FIG. 24, arepreferable designed to match the high impedance of the piezos. Knownelectronic principles may be used, such as matching the input impedanceof the receiver circuit to the impedance of the receive transducer.

FIG. 24 illustrates an edge wave touch sensor system 300 formed inaccordance with an embodiment of the present invention. The touch sensorsystem 300 comprises the substrate 20 having the touch surface 24 andsidewalls 32 (not shown). For clarity, the edges 22 have been indicatedas edges 306, 308, 310 and 312.

A controller 112 supplies electrical signals to transmitting transducers302 and 304 via electrical connections 110 to excite the piezos of thetransmitting transducers 302 and 304. Gratings 92 and 94 convert piezovibrations to a first acoustic mode, such as edge wave 314 travelingalong edge 306 and edge wave 316 traveling along edge 308, respectively,as indicated by arrows. The edge wave 314 is converted by reflectivearray 318 into Rayleigh wave 320. The Rayleigh wave 320 travels as asurface acoustic wave bound to the surface 24 until it encountersreflective array 322, where it is converted back into an edge wave 324and travels along the edge 310 in the direction indicated by an arrowwhere it can be detected by receiving transducer 326. Similarly, theedge wave 316 is converted by reflective array 328 into Rayleigh wave330. The Rayleigh wave 330 travels as a surface acoustic wave bound tothe surface 24 until it encounters reflective array 332, where it isconverted back into an edge wave 334 and travels along the edge 312 inthe direction indicated by an arrow where signal amplitudes of the edgewave can be detected by receiving transducer 336. Electrical connections114 are made so that receiving transducers 326 and 336 can supplyelectrical signals back to the controller 112. Perturbations (e.g., atouch with a finger or stylus) to the touch surface 24 can then bedetected as perturbations in the signals from the edge wave on thereceiving edge, and a location associated with the perturbation can bedetermined based on the time the perturbation is detected in thereceived signal. The electrical connections 110 and 114 can comprisecable harnesses.

A touch sensitive region 108 is formed on the touch surface 24 andcomprises essentially the entire touch surface 24 because the reflectivearrays 318, 322, 328, and 332 and transducers 302, 304, 326, and 336 maybe formed along and/or joined to a very narrow outer periphery 116 ofthe sensor substrate 20, and in many cases can be made on and/or joinedto the sidewalls 32 of the substrate 20. The outer periphery 116 of thetouch surface 24 that is needed for the generation and detection of theone-dimensional edge waves can be as little as 1 mm.

Alternatively, the surface acoustic wave (e.g., two-dimensional SAW) canbe detected directly after traversing at least a portion of the touchsensitive region 108 without being converted to an edge wave to identifythe presence and location of perturbations to the touch sensitive region108 of the touch surface 24.

FIG. 24 may be modified to provide two-dimensional touch positioncoordinates using two transmit/receive transducers as discussedpreviously. In addition, many other touchscreen geometries using edgewaves are possible, including touchscreen designs with non-orthogonalacoustic paths that can be adapted for use with edge waves.

FIG. 25 illustrates a touch panel 350 in accordance with in embodimentof the present invention. Clean edges 356-362 are formed on thesubstrate 20. Reflector elements 364 and 366 are formed on the sidewall32 or touch surface 24 proximate two of the edges 356 and 362. Thereflector elements 364 are illustrated as being formed on the sidewall32 proximate the edge 356 and the reflector elements 366 are illustratedas being formed on the touch surface 24 proximate the edge 362. Piezos352 and 354 are used to both transmit and receive edge wave information.

Only one piezo 352 or 354 can be actively transmitting or receiving atone time. A controller 368 may communicate with each of the piezos 352and 354 via electrical connections 370 and 372. The controller 368 mayhave switches 374 and 376 to control which piezo 352 or 354 is connectedto a signal generator 378 for transmitting a signal or an electronicsmodule 380 for receiving and decoding a signal. The controller 368 mayalternate between the piezos 352 and 354, wherein the piezo 352 maytransmit and receive a signal followed by the piezo 354 transmitting andreceiving a signal. Alternately, electrical connections 370 and 372 mayeach be provided with one of two identical circuits each with atransmit/receive mode switch.

Upon activation, the piezo 352 transmits an edge wave in the directionof arrow 382. The edge wave encounters the reflector elements 364 and isconverted to a SAW coupled to the surface of the touch surface 24 andtransmitted in the direction of arrow 384. A significant fraction of SAWpropagating in direction 384 will be reflected by edge 360.Alternatively, one or more reflective strips 386 may be placed one-halfwavelength apart on the touch surface 24 proximate and parallel to theedge 360. The edge 360 and/or the reflective strips 386 reflect the SAWby 180° in the direction of arrow 388. When the SAW encounters the edge356 and the reflector elements 364, the SAW is converted to an edge wavetransmitted in the direction of arrow 390. The edge wave is detected bythe piezo 352 and the electrical signal is read by the controller 368via the electrical connection 370.

The controller 368 then transmits an electrical signal from the signalgenerator 378 over the electrical connection 372 to excite piezo 354.The piezo 354 generates an edge wave traveling along the edge 362 in thedirection of arrow 392. As the edge wave encounters the reflectiveelements 366, the edge wave is converted to a SAW traveling across thetouch surface 24 in the direction of arrow 394. The SAW is reflected180° by the edge 358 and/or one or more reflective strips 396. Thereflected SAW travels in the direction of arrow 398, encounters the edge362 and reflective elements 366, and is converted to an edge wavetraveling in the direction of arrow 400. The piezo 354 detects the edgewave and sends an electrical signal over the electrical connection 372to the controller 368.

FIG. 31 illustrates an alternative edge wave touch sensor system formedin accordance with an embodiment of the present invention. A singletransducer 602 operates in both transmit and receive modes to providetwo-dimensional touch coordinate information while utilizing a verynarrow border region of the touch surface 24. The transducer 602 may beany transducer design capable of transmitting and receiving edge waves,such as transducer designs previously discussed.

The substrate 20 is formed having clean edges 604-610. A rounded corner612 is formed where the edges 604 and 606 intersect. The rounded corner612 is also formed having a substantially clean edge, and may have anangle of approximately 90°. Reflector arrays 614 and 616 are formed onthe edges 604 and 606, respectively. An absorbing damper 618 is formedon one end of the sidewall 32 proximate the edge 608 and proximate oneend of the reflective array 616. It should be noted that the waveguideproperties of the edge enable a very simple and efficient way toredirect edge waves by 90° between the reflector arrays 614 and 616 foracquiring both X and Y touch data, namely, the sidewall 32 may be formedhaving a simple quarter-circle shaping of the sidewall 32 andcorresponding edges 604 and 606.

The transducer 602 transmits an edge wave in the direction of arrow 620along the edge 604. A portion of the transmitted edge wave is scatteredby the reflector array 614 and traverses the touch surface 24 in thedirection of arrow 622 as a Rayleigh wave. The wave is reflected by 180°in the direction of arrow 624 and again by the reflector array 614 inthe direction of arrow 626 to be received by the transducer 602. Thisportion of the transmitted edge wave is received relatively early intime and provides a measurement of the X coordinate of a touch.

Another portion of the transmitted edge-wave from the transducer istransmitted through the reflector array 614, follows the rounded corner612 and encounters the reflector array 616. The edge-wave power ispartially scattered at 90° as a Rayleigh wave in the direction of arrow628 and traverses the touch surface 24 as a Rayleigh wave. The wave isreflected by 180° by the edge 610 in the direction of arrow 630, andreflected by the reflector array 616 and received by the transducer 602.This portion of the transmitted edge-wave is received relatively late intime and provides a measurement of the Y coordinate of a touch. Anyremaining portion of the transmitted edge-wave that is transmittedthrough both the reflector arrays 614 and 616 may be eliminated with theabsorbing damper 618.

FIG. 26 illustrates a touch panel 402 in accordance with an embodimentof the present invention. The touch panel 402 comprises a substrate 20with sidewalls 32 as discussed previously. Clean edges 404-410 have beenformed at an intersection between the planes of each of the sidewalls 32and the touch surface 24. The substrate 20 is formed having onedimension of the touch surface 24 greater than the other. For example,the substrate 20 along the X dimension is longer than in the Ydirection.

Acoustic waves traveling longer acoustic path lengths in a touch sensoror touch sensor system will experience more loss than those travelingshorter acoustic path lengths. Therefore, to make touch sensitivityrelatively uniform throughout the touch sensitive region of a touchsensor, it is often desired to effect an equalization of signalsresulting from acoustic waves traveling different acoustic path lengthsso that signal levels are approximately independent of acoustic pathlength.

Reflector elements 420, 422 and 424 have been formed proximate the edges406, 410 and 404, respectively. As discussed previously, the reflectorelements 420-424 may be formed as regularly spaced grooves orprotrusions on the sidewalls 32 and/or the touch surface 24. Optionally,one or more reflective strips 426 may be formed on the touch surface 24proximate the edge 408.

The touch panel 402 uses three piezos 412, 414 and 416. The piezo 412may be used to transmit signals while the piezo 414 is used to receivesignals. A signal generator 428 within controller 418 transmits a signalover electrical connection 430. The transmitting piezo 412 launches anedge wave along edge 406 in the direction of arrow 432. The edge wave ispartially reflected by the reflector elements 420 and is converted to aSAW moving across the touch surface 24 in the direction of arrow 434.The SAW is converted to an edge wave by the reflector elements 422 andtravels along the edge 410 in the direction of arrow 436. The piezo 414detects the edge wave and sends an electrical signal to the controller418 via electrical connection 438.

The piezo 416 is used for both transmitting and receiving signals. Thismay be accomplished as discussed previously in connection with FIG. 25and the controller 368. The piezo 416 is excited by an electrical signalfrom the signal generator 428 of the controller 418 via electricalconnection 440. The piezo 416 launches an edge wave along edge 404 inthe direction of arrow 442, which is partially reflected by thereflector elements 424 in the direction of arrow 444 as a SAW. The SAWis reflected 180° by the reflective strip 426 and/or the edge 408 in thedirection of arrow 446. The SAW is reflected by the reflector elements424 and converted to an edge wave propagating in the direction of arrow448. The edge wave is detected by the piezo 416 and an electrical signalis sent to the controller 418 over the electrical connection 440.

The touch panel 402 utilizes one piezo 416 with reflector elements 424and the edge 408 (and optionally the reflector strip 426) to detecttouch events along the X axis. To detect touch events along the Y axis,the two piezos 412 and 414 and the reflector elements 420 and 422 areused. Therefore, the SAW traverses the touch surface 24 along the X axisonly once, while the SAW traverses the touch surface 24 along the Y axistwice.

FIG. 27 illustrates a large touch panel 450 comprising four piezos452-458 in accordance with an embodiment of the present invention. Thetouch panel 450 may comprise a large touch surface 24 on the substrate20. Therefore, the distance the waves have to travel becomes increasinglonger and the signal experiences increased attenuation. For a giventouch panel size, the design in FIG. 27 minimizes the maximum pathlength while having a single transducer at each corner. Note that atmost one transducer of the designs in FIGS. 15-18 and 23 can be placedat each corner of the substrate 20.

The piezos 452-458 are mounted at different corners of the substrate 20and thus do not physically interfere with each other. Each of the piezos452-458 both transmit and receive signals as discussed previously inFIG. 25, and therefore the controller 418 will not be further discussed.

The substrate 20 is formed having clean edges 460-466. Reflectorelements 470-476 are formed proximate each of the edges 460-466 along alength of approximately one-half of each of the edges 460-466 closest tothe piezos 452-458. Reflective strips 494-498, if present, may be formedon the touch surface 20 parallel to the edge 466 and spaced apart by adistance of approximately one-half surface acoustic wavelength. Thereflective strips 494-498 are formed along approximately one-half of thelength of the edge 466 where the reflector elements 476 are not present,or the half of the edge 466 furthest away from the piezo 456. Additionalreflective strips are formed on the touch surface 20 parallel to each ofthe edges 460-464 in the same manner.

When the piezo 452 is excited, the piezo 452 launches an edge wave alongthe edge 462 in the direction of arrow 478. The edge wave is partiallyreflected by the reflector elements 472 and converted to a SAW travelingacross the touch surface 24 in the direction of arrow 480. The SAW isreflected by 180° in the direction of arrow 482 by the reflective strips494-498 and/or the edge 466. The SAW is reflected 90° by the reflectorelements 472 in the direction of arrow 484 and received by the piezo452. Therefore, the piezo 452 detects a signal representative of a Ycoordinate of one-half of the touch surface 24, such as area 486.

The piezos 454, 456 and 458 each send and receive signals in the mannerdescribed for piezo 452, detecting a signal over an area ofapproximately one-half of the touch surface 24. The piezo 454 detects asignal representative of an X coordinate of an area 488. The piezo 456detects a signal representative of a Y coordinate of an area 490. Thepiezo 458 detects a signal representative of an X coordinate of an area492. Therefore, compared to touch panels that use two piezos to transmitand receive signals, the touch panel 450 uses four piezos 452-458 whichreceive signals from a signal path reduced in length compared to the twopiezo geometry. The edge waves do not have to travel as far and largertouch panels 450 may be implemented. Also, there is no physicalinterference between piezos 452-458 as each of the piezos 452-458 ismounted on a different corner of the substrate 20.

FIG. 32 illustrates a touch sensor 640 wherein a single transmittransducer 642 generates X and Y signals in accordance with anembodiment of the present invention. The substrate 20 is formed havingclean edges 646-652 as previously discussed. The transmit transducer 642is mounted on the second surface 28 of the substrate 20 and launches anedge wave in the direction of arrow 654 up a vertical edge 644 whichforms the intersection of two sidewalls 32. At a vertex 656 formed ofthe vertical edge 644 and the two edges 646 and 648, the incidentvertically propagating edge wave splits into two horizontallypropagating edge waves traveling in the directions of arrows 658 and660.

The horizontally propagating edge wave traveling in the direction ofarrow 658 encounter a transmit reflector array 662 (X direction) whichpartially scatters the edge wave by 90° and is converted to Rayleighwaves transmitted through the touch surface 24 in the direction of arrow666. The Rayleigh waves are subsequently received by the X receivereflector array 668, converted to edge waves that are directed in thedirection of arrow 672 and received by a transducer 674.

Likewise, the horizontally propagating edge wave traveling in thedirection of arrow 660 encounters a transmit reflector array 664, ispartially scattered by 90° and converted to Rayleigh waves transmittedthrough the touch surface 24 in the direction of arrow 676. The Rayleighwaves are received by the Y receive reflector array 670, converted toedge waves that are directed in the direction of arrow 678 and receivedby a transducer 680. Therefore, the X and Y signals share a common burst(from transducer 642) but have distinct receive signals from distinctreceive transducers (674 and 680). Alternatively, the acoustic paths maybe reversed so that distinct X and Y transmit transducers maysequentially excite acoustic paths received by a common receivertransducer.

FIG. 33 illustrates an alternative touch sensor 690 wherein a singletransmit transducer 692 generates X and Y signals in accordance with anembodiment of the present invention. In FIG. 33, the transmit transducer692 and receive transducers 694 and 696 may be formed and/or attached tothe second surface 28 of the substrate 20, allowing increasedflexibility when designing a system using the touch sensor 690.Quarter-circle bends 698 and 700 guide the initially horizontaledge-waves into a vertical direction as needed to be received by thetransducers 694 and 696 mounted on the bottom surface of the substrate20.

FIG. 34 illustrates a geometry of the substrate 20 near the commontransmit transducer 692 in accordance with an embodiment of the presentinvention. The transducer 692 launches an edge wave in the direction ofarrow 704 up a vertical edge 702. The vertical edge 702 forms two curvededges 706 and 708, and the edge wave splits to form two edges wavespropagating in the directions of arrows 710 and 712. Alternatively, thegeometry may be the same as illustrated in FIG. 32. Experimental andsimulation studies may be used to determine the geometry of thesubstrate corner that most efficiently splits the transmitted acousticenergy between the X and Y signal paths. As with FIG. 32, the roles oftransmit and receive transducers may be swapped in the embodiment ofFIGS. 33 and 34.

FIG. 28 illustrates a block diagram of a touch monitor 500interconnected with a computer 502 in accordance with an embodiment ofthe present invention. The computer 502 runs one or more applications,such as in a factory, a retail store, a restaurant, a medical facilityand the like. The computer 502 may be used for calibration and testingin a factory setting, for example, and may comprise a display 504 and auser input 506 such as a keyboard and/or a mouse. Multiple touchmonitors 500 may be interconnected with the computer 502 over a network.

A monitor 508 comprises components for displaying data on a display 510.The display 510 may be an LCD, CRT, plasma, photographic image and thelike. A touchscreen 512 is installed proximate the display 510. Thetouchscreen 512 receives input from a user via a finger touch, a stylus,and the like. The touchscreen 512 may be formed of the substrate 20 andhave a very narrow border 536. The border 536 may be the width of anedge wave as discussed previously.

A monitor cable 514 connects the monitor 508 with a monitor controller516. The monitor controller 516 receives video information from thecomputer 502 over video cable 518. The video information is received andprocessed by the monitor controller 516, then transferred to the monitor508 over the monitor cable 514 for display on the display 510. It shouldbe understood that the monitor 508 and the monitor controller 516 may behardwired together or interconnected such that the monitor cable 514 isnot required. The monitor controller 516 comprises components such as aCPU 520 and a memory 522.

A touchscreen cable 524 interconnects the touchscreen 512 with atouchscreen controller 526. The touchscreen controller 526 sends andreceives information to and from the computer 502 over touch data cable528. Touch information is received by the touchscreen 512, transferredover the touchscreen cable 524 to the touchscreen controller 526, andthen sent over the touch data cable 528 to the computer 502. Thetouchscreen controller 526 comprises components such as a CPU 530 andmemory 532.

A monitor housing 534 may enclose the monitor 508, the monitor andtouchscreen cables 514 and 524, and the monitor and touchscreencontrollers 516 and 526. The monitor housing 534 may enclose the border536 of the touchscreen 512, securing the touchscreen 512 and preventingoutside interference with the edge wave, reflectors, transducers,piezos, and the like. For example, it may be desirable to integrate andseal an acoustic touch sensor such as the touchscreen 512 to otherequipment such as the monitor housing 534. The seal can prevent theingress of water or other contaminants to the transducers and edge-wavepropagating edges, as well as internal components of a touch displaysystem containing the touch sensor. As the border 536, including thetransducers for generating and receiving acoustic waves and thereflective arrays for directing the acoustic waves, is narrow, then thetotal area that must be sealed is reduced when compared to previousmonitors having wider borders. Because of the very narrow border 536made possible by using edge waves, the sealing may be facilitated, forexample, by using sealing materials which may be printed ormicro-dispensed onto the substrate 20 with controlled registration andnarrow seal width. Sealing materials that are heat cured and bonded tothe substrate 20 can be used.

By way of example only, the monitor housing 534 may be for a stand alonemonitor. Optionally, the monitor housing 534 may be omitted if the touchmonitor 500 is installed within a kiosk or other enclosure. The videoand touch data cables 518 and 528 may be separate cables or packagedtogether. The video and touch data cables 518 and 528 extend from themonitor housing 534 to the location of the computer 502.

The memories 522 and 532 store data including Extended DisplayIdentification Data (EDID) data. EDID data may include information aboutthe monitor 508 and touchscreen 512 such as a vender or manufactureridentification number, maximum image size, color characteristics,pre-set timings, and frequency range limits. Optionally, memories 522and 532 may be combined and provided with one of monitor and touchscreencontrollers 516 and 526, to form a single common memory module whichstores the EDID for both of the monitor 508 and touchscreen 512.Optionally, the touchscreen and monitor controllers 516 and 526 may becombined to form a single common controller for the touch monitor 500.

It should be understood that the touch monitor 500 implementation isonly one of many possible implementations of the acoustic touch sensor.For example, a metal, such as aluminum, may be used to form thesubstrate to create a table accepting touch input. Edge waves travel oncurved edges, and thus may be propagated around an edge of a roundobject, such as a round table top or a cylinder. FIG. 29 illustrates anexample of a round table top 550 in accordance with an embodiment of thepresent invention. The round table top 550 may be made of glass or metalwith a clean edge 552 around its perimeter, a square touch area 554, andreflective arrays 556-562 and transducers 564-570 fabricated on theperimeter edge 552 as needed to support the acoustic paths shown. FIG.35 illustrates an alternative geometrical option in accordance with anembodiment of the present invention. A solid or hollow cylinder 720 hasa clean 90° edge 722 with circular geometry on which is fabricated atransmit/receive transducer 728, a reflective array 726, and optionallya edge-wave beam dump, or damper 730. An edge-wave from the transducer728 is scattered downward by 90° and mode converted to a downwardpropagating Rayleigh wave in the direction of arrow 732. At the bottomof the cylinder 720 the edge-wave is reflected by 180° in the directionof arrow 734 and the acoustic path retraces its path back to thetransducer 728. The damper 740 may be provided to absorb any edge-wavepower scattered by the reflective array 726 onto the top horizontalsurface 724. Such a sensor provides an angular coordinate of a touchevent about the axis of the cylinder 720. (The array design principlesof U.S. Pat. No. 5,854,450, incorporated herein by reference, can bealso be applied to edge-wave touch sensor designs to enable generalizedtouch sensor geometries.) Track pads for museum exhibits and othergeneral public applications may also be implemented, wherein substrate20 is of a robust stainless steel construction of circular or evenhemi-spherical geometry. Therefore, the geometry of the acoustic touchsensor is not limited to a square or rectangular flat surface, but maybe used to form a large number of different products such as touchsensitive robot surfaces for collision detection. Also, the size of theimplementation is not limited, as larger size areas may be detectedusing a variety of transducer and reflector combinations.

As stated previously, acoustic waves traveling longer acoustic pathlengths in a touch sensor or touch sensor system will experience moreloss than those traveling shorter acoustic path lengths. Therefore, tomake touch sensitivity relatively uniform throughout the touch sensitiveregion of a touch sensor, it is often desired to effect an equalizationof signals resulting from acoustic waves traveling different acousticpath lengths so that signal levels are approximately independent ofacoustic path length. Signal equalization may be accomplished, forexample, by varying the density of reflector elements along the acousticpaths; the reflector element height or depth along the reflective array;the length of reflector elements; the reflector element length within anarray; and the distance between a reflective array and an acoustic beam.In addition, the number of transducers used to transmit and/or receive,and the area of the touch screen each transducer sends and/or receivessignals from may be adjusted to account for size and/or shape of thetouch object.

It should be understood that the above-described arrangements ofapparatus and method are merely illustrative, and that other embodimentsand modifications may be made without departing from the spirit andscope of the claims.

1.-20. (canceled)
 21. A shear-mode transducer for generating or receiving an acoustic edge wave in a touch sensor having a substrate with a first surface having a touch region and a second surface intersecting the first surface along a first edge, the acoustic edge wave propagating along the first edge, the shear-mode transducer mounted on the substrate on the second surface, the shear-mode transducer comprising: a shear-mode piezoelectric element, the shear-mode piezoelectric element providing shear motion in a direction relative to a plane of the second surface defined by X and Y axes so as to couple to the acoustic edge wave; and a first electrode and a second electrode disposed on the shear-mode piezoelectric element to provide an active region of the shear-mode piezoelectric element, said active region comprising a cross-sectional area of the acoustic edge wave.
 22. The shear-mode transducer of claim 21, wherein the second surface comprises a sidewall of the substrate, wherein the second sidewall is perpendicular to a propagation direction of the first acoustic wave.
 23. The shear-mode transducer of claim 21, wherein the shear-mode piezoelectric element has been poled to provide the shear motion in the direction comprising an approximately 45 degree in the plane.
 24. The shear-mode transducer of claim 23, the shear-mode piezoelectric element comprising a front and a back surface, the first electrode covering a portion of the front surface, the second electrode covering a substantial part of the back and front surfaces, the active region corresponding to an area of the shear-mode piezoelectric element where the first and second electrodes overlap
 25. The shear-mode transducer of claim 21, the shear-mode transducer being bonded to the substrate, the bonding corresponding to a portion of the active region and providing strong acoustic coupling between the substrate.
 26. The shear-mode transducer of claim 21, wherein the active region has a size less than one-wavelength squared of the first acoustic wave.
 27. The shear-mode transducer of claim 24, the first and second electrodes on the front surface of the shear-mode piezoelectric element configured for receiving attachments to first and second electrical connections for exciting the shear-mode piezoelectric element, wherein the front surface is covered approximately equally by the first and second electrodes which are separate.
 28. The shear-mode transducer of claim 21, the shear-mode piezoelectric element comprising front and back surfaces, a depth, a first side; a second side; the first side and second side not intersecting but being joined by a notched corner, the notched corner also intersecting each of the front and back surfaces, the shear-mode piezoelectric element being poled in a direction perpendicular to the plane; and first and second electrodes formed on first and second edges, the first and second electrodes receiving attachments to first and second electrical contacts for exciting the piezoelectric element.
 29. The shear-mode transducer of claim 28 wherein the depth comprises one-half of a bulk shear wave wavelength.
 30. The shear-mode transducer of claim 28 wherein the notched corner has an angle of approximately 45 degrees with respect to the first and second sides.
 31. The shear-mode transducer of claim 21, the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the first acoustic wave.
 32. The shear-mode transducer of claim 24, the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the first acoustic wave.
 33. The shear-mode transducer of claim 28, the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the first acoustic wave.
 34. The shear-mode transducer of claim 29, the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the first acoustic wave.
 35. The shear-mode transducer of claim 30, the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the first acoustic wave.
 36. The shear-mode transducer of claim 24, wherein the second electrode wraps around the shear-mode piezoelectric element from the front surface to the back surface. 